The problem with the powder is that it's hard for them to eat it if you give it to them plain in a seperate feeder. And if you mix into their feed you'd want to be careful not to mix too much since they won't be able to separate it out if they don't want it.
I've never found it necessary to go so far. I keep a pan in the oven that I toss the shells into. When ever I bake something I put the pan back in after I'm done so the residual heat dries the shells well. When the pan is full I pour them intio an old #10 can and crush the up with a potato masher. No need to finely crush them, just good and crumbled. When the can is full I take it to the feed room where I mix a couple of handfuls into each tube feeder of grain. The pieces are big enough that the hens can easily eat them if they want to or ignore them if their calcium appetite has been slaked already.
ok Punkin peep ..... you all have convinced me.... I am now saving and drying eggshells and crumbling them up... I too keep fake eggs in nest so that should take care of that.....